Hi,
I am building a 2 story house (in Israel) using an engineered “I” joist system for the ceiling/floor systems. This includes the second floor ceiling which is also the attic floor. The attic is going to be used as living space and the roof will have two dormers built into it. It will be a hip roof.
My question is, the engineered plans (sent from Canada with the joists) for the upper attic floor (sheathed with T&G 18mm OSB) include a rim joist around the perimeter of the floor. Usually I would frame the roof fastening the rafters’ birds mouth to the double top plate and fastening it to an adjacent joist. However, with the addition of a rim board, I am wondering what would be the best way to frame the roof? I don’t know if it would be a good idea to get rid of the rim board or possibly place a 2-by plate on the OSB and fasten the rafters just to that, which would mean losing the strength of tying the rafters to the joists.
I would really appreciate feedback on this question!
Thanks
Nagar1
Replies
Adding a 2x plate on top of the subfloor is how I've seen it done most of the time.
nagar
I hunted for a detail for you but came up empty. Contact your supplier, they probably just sent you their generic detail package.
Boss mentions what I did the only time I've used I-joists (15 yrs ago). I-joists, squash blocks at the ends and 3/4 ply rim. After sheeting the floor, 2x4 top plate with rafters cut and fitted to that. I'm sure there's now more engineering on the connection than just toenailing / blocking. That's what you need to find to satisfy both you and the inspector.
Don't skip the rim
I wouldn't skip the rim joist without an engineer telling me to -- they're engineered assemblies.
This detail doesn't show a subfloor on top of the ceiling joists, but it shows the raised plate which your rafters would land on. This makes more room for insulation at the critical spot where roofs meet walls. Though ice damming is probably not much of a problem in Israel.
Hi Dan
Good to see you haven't forgotten about BT altogether!
Just wanted to echo what Dan said about not skipping the rim joist. He's 100% right, and I missed that in my first post.
I joist - rimboard
The rimboard is an integral part of the joist design. You cannot delete it.
Install the subfloor and add a 2x support on top of the subfloor. Nail/screw the support solidly into the I joist. Use hurricane straps or angle brackets to secure the rafters on the 2x support.
Note that the anglecut/birdsmouth must have full support. If you are using I joists for rafters the engineering detail will explain it more
Have you thought of attac trusses?
It is a pretty ccommon technique here to frame that upper by nailing a plate down over the 18mm subfloor and then treat that like the top plate of the wall you are used to setting your rafters on